The ViePHEP relies on a theoretical model that comprises several (surmised) relationships between theoretical constructs, such as socio-economic status (SES) or a set of preferences for health policies and allocations in health care. These theoretical constructs follow an underlying logic, which means their interconnections follows a certain direction, i.e. there is action and reaction. However, these constructs should not remain elusive or abstract. Instead they are operationalised as one or several variables each. For instance, SES becomes palpable, measureable and also replicable through the variables household income, occupation, wealth, debt and some other concrete metrics. Ultimately, each variable, every combination of variables and each construct should conform to the criteria of validity and reliability.